Short AV interval VDD pacing does not prevent tilt induced vasovagal syncope in patients with cardioinhibitory vasovagal syndrome

Temporal relationship between haemodynamic changes and activation of closed-loop stimulation during a tilt-induced vasovagal syncope

AIMS

A dual-chamber pacemaker with closed-loop stimulation (CLS) mode is effective in reducing syncopal recurrences in patients with asystolic vasovagal syncope (VVS). In this study, we explored the haemodynamic and temporal relationship of CLS during a tilt-induced vasovagal reflex.

METHODS AND RESULTS

Twenty patients underwent a tilt test under video recording 3.9 years after CLS pacemaker implantation. Three patients were excluded from the analysis because of no VVS induced by the tilt test (n = 1) and protocol violation (n = 2). In 14 of the remaining 17 patients, CLS pacing emerged during the pre-syncopal phase of circulatory instability when the mean intrinsic heart rate (HR) was 88 ± 12 b.p.m. and systolic blood pressure (SBP) was 108 ± 19 mmHg. The CLS pacing rate thereafter rapidly increased to 105 ± 14 b.p.m. within a median of 0.1 min [inter-quartile range (IQR), 0.1-0.7 min] when the SBP was 99 ± 21 mmHg. At the time of maximum vasovagal effect (syncope or pre-syncope), SBP was 63 ± 17 mmHg and the CLS rate was 95 ± 13 b.p.m. The onset of CLS pacing was 1.7 min (IQR, 1.5-3.4) before syncope or lowest SBP. The total duration of CLS pacing was 5.0 min (IQR, 3.3-8.3). Closed-loop stimulation pacing was not observed in three patients who had a similar SBP decrease from 142 ± 22 mmHg at baseline to 69 ± 4 mmHg at the time of maximum vasovagal effect, but there was no significant increase in HR (59 ± 1 b.p.m.).

CONCLUSION

The reproducibility of a vasovagal reflex was high. High-rate CLS pacing was observed early during the pre-syncopal phase in most patients and persisted, although attenuated, at the time of maximum vasovagal effect.

REGISTRATION

ClinicalTrials.gov identifier: NCT06038708.

Cardiac Pacing in Cardioinhibitory Reflex Syncope: Clinical Use of Closed-loop Stimulation

Cardiac pacing has been studied extensively in patients with reflex syncope over the past two decades. The heterogeneity of the forms and clinical manifestations of reflex syncope explain the controversial results of older randomised clinical trials. New evidence from recent trials has changed medical practice, now leading to clear indications for pacing in patients with asystolic syncope documented during carotid sinus massage, implantable cardiac monitoring or tilt testing. Given that recent trials in reflex syncope have been performed using the closed-loop stimulation algorithm, the authors will briefly discuss this pacing mode, review hypotheses about the mechanisms underlying its activation during syncope and provide practical instructions for programming and troubleshooting.

Pacing in vasovagal syncope: Physiology, pacemaker sensors, and recent clinical trials-Precise patient selection and measurable benefit

The role of pacing in vasovagal syncope (VVS) is considered from a physiological basis. Most VVS patients lose consciousness due to hypotension before severe bradycardia/asystole occurs. Patients who benefit from dual-chamber pacing typically are older with highly symptomatic, late-onset, frequent and severe syncope with short/no prodrome and documented severe cardioinhibition. Tilt testing is of value in patients with recurrent unexplained syncope to identify important hypotensive susceptibility stemming from reduced venous return and stroke volume (SV). A negative tilt test in vasovagal patients with spontaneous asystole documented by an implantable/insertable loop recorder is associated with lower syncope recurrence rates after pacemaker implantation. Pacing may be more effective if triggered by sensor detection of a parameter changing earlier in the reflex than bradycardia when SV may still be relatively preserved. In this regard, detection of right ventricular impedance offers promise. Conservatism is recommended, limiting pacing in VVS to a small subset of symptomatic older patients with clearly documented cardioinhibition and paying particular attention to the timing of loss of consciousness in relation to asystole/bradycardia. Understanding VVS physiology permits application of well-timed, appropriate pacing that yields benefit for highly symptomatic patients.

Reproducibility of the head-up tilt test results in children with vasovagal syncope

BACKGROUND

This prospective study aims to investigate the reproducibility of HUTT results in children with typical history of vasovagal syncope.

METHODS

Between October 1996 and October 1999, 58 children with a history of typical vasovagal syncope attacks were evaluated with head up tilt test (HUTT). The table was tilted to 60 degrees and the patients were monitored for heart rate and blood pressure changes during 45 min. No provocative agents were used. The test was repeated a week later at a similar setting.

RESULTS

Of 58 patients, 39 had positive and 19 had negative response during the initial test. During the second test, the positive response was reproduced in 29 cases (50%), and the negative response was reproduced in 16 cases (28%). Ten patients (17%) with an initial positive test had a negative second test. A negative test became positive only in three patients (5%). There were 12 vasodepressor, four cardioinhibitor and 23 mixed responses among the initial tests. Only in four patients did the type of the response change from vasodepressor to a mixed type during the second test. The reproducibility of a positive tilt test was 74.4% (29/39), the negative tilt test was 84.2% (16/19), and the overall reproducibility of the HUTT was 77.6% (45/58).

CONCLUSIONS

Unprovoked HUTT in children is reproducible when repeated on different days and similar settings and the results are comparable to the ones with adult patients.

Cardiac pacing. A review

Pacing is a field of rapid clinical progress and technologic advances. Clinical progress in the 1990s included the refinement of indications for pacing as well as the use of pacemakers for new, nonbradycardiac indications, such as the treatment of cardiomyopathies and CHF and the prevention of atrial fibrillation. Important published data and studies in progress are shedding new light on issues of pacing mode selection, and they may influence future practice significantly. Important technologic advances include development of new rate-adaptive sensors and sensor combinations and the evolution of pacemakers into sophisticated diagnostic devices with the capability to store data and ECGs. Automatic algorithms monitor the patient for appropriate capture, sensing, battery status, and lead impedance, providing better patient safety and pacemaker longevity.

Exercise-induced neurocardiogenic syncope: clinical data, pathophysiological aspects, and potential role of tilt table testing

The evaluation of syncope occurring during exercise or occurring spontaneously in highly trained individuals presents a unique diagnostic challenge. It is of critical importance to exclude potential life-threatening disorders such as hypertrophic cardiomyopathy, long QT syndrome, right ventricular dysplasia, anomalous coronary artery distribution, valvular heart disease, myocarditis, or exercise-induced arrhythmia. This review is not directed towards identifying, treating, or determining athletic eligibility of individuals with such disorders. Rather, we endeavour to discuss the pathophysiology of exercise-induced neurocardiogenic syncope and to address the role of head upright tilt testing in evaluating syncope in athletic individuals in whom proper evaluation has excluded the presence of ischaemic heart disease or primary structural or electrical heart disease.

Cardiac pacing for severe childhood neurally mediated syncope with reflex anoxic seizures

OBJECTIVE

To determine whether permanent cardiac pacing could prevent syncope and seizures in children with frequent severe neurally mediated syncope, and if so whether dual chamber pacing was superior to single chamber ventricular pacing.

METHODS

Dual chamber pacemakers were implanted into 12 children (eight male, four female) aged 2-14 years (median 2.8 years) with frequent episodes of reflex anoxic seizures and a recorded prolonged asystole during an attack. The pacemaker was programmed to sensing only (ODO), single chamber ventricular pacing with hysteresis (VVI), and dual chamber pacing with rate drop response (DDD) for four month periods, with each patient allocated to one of the six possible sequences of these modes, according to chronological order of pacemaker implantation. The parent and patient were blinded to the pacemaker mode and asked to record all episodes of syncope or presyncope ("near miss" events). The doctor analysing the results was blinded to the patient and pacemaker mode.

RESULTS

One patient was withdrawn from the study after the pacemaker was removed because of infection. In the remaining children, both dual chamber and single chamber pacing significantly reduced the number of syncopal episodes compared with sensing only (p = 0.0078 for both). VVI was as effective as DDD for preventing syncope, but DDD was superior to VVI in reducing near miss events (p = 0.016).

CONCLUSIONS

Permanent pacing is an effective treatment for children with severe neurally mediated syncope and reflex anoxic seizures. VVI is as effective as DDD in preventing syncope and seizures, but DDD is superior in preventing overall symptoms.

Contribution of head-up tilt testing and ATP testing in assessing the mechanisms of vasovagal syndrome: preliminary results and potential therapeutic implications

BACKGROUND

In patients with vasovagal syndrome, head-up tilt testing may reproduce symptoms generally associated with vasodepression. Recent research suggests ATP testing identifies patients with abnormal vagal cardiac inhibition. This preliminary study examined the joint contribution of both tests in identifying underlying mechanisms in the general population with vasovagal syndrome.

METHODS AND RESULTS

Both tests were performed in random order during 1 session and outside of predominant sympathetic periods in 72 patients hospitalized for syncope (n=56) or presyncope (n=16) for whom no cardiac or extracardiac cause was found. For passive and isoproterenol-provocative tilt testing by standard protocol, reproduction of symptoms defined a positive test. The ATP test consisted of injecting ATP 20 mg IV at bedside, continuously monitoring ECG and blood pressure; a vagal cardiac pause >10 seconds defined a positive test. For most patients (64%), >/=1 test was positive. Of the 41 patients (57%) with a positive tilt test (either passive or provoked by isoproterenol), 32% had cardiac disease; none had significant bradycardia (<50 bpm). Of the 8 patients (11%) with a positive ATP test, 62% had cardiac disease; the probability of a positive result increased with age (P=0.015). Both tests were positive in 3 patients and negative in 26 patients; the tilt and ATP test results were uncorrelated (P=0.28).

CONCLUSIONS

Results suggest tilt and ATP tests individually and jointly determine the mechanism of vasovagal symptoms in most patients and that vagal cardiac inhibition increases with age.

Role of endogenous opioids in syncope induced by head-up tilt test and its relationship with isoproterenol-dependent and isoproterenol-independent neurally-mediated syncope

This study was designed to evaluate the role of endogenous opioids in neurally-mediated syncope. Head-up tilt test was performed on 35 patients with syncope of unknown origin. Plasma beta-endorphin was measured (1) at baseline, (2) at the end of tilt test or at time of syncope, (3) 15 min before isoproterenol-test, (4) at the end of the isoproterenol-test or at time of syncope. Subjects with a positive tilt testing showed a larger rise in plasma beta-endorphin concentrations at time of syncope (baseline 13.7+/-8.0 vs. syncope 41.4+/-26.4 pmol l(-1); P<0.01). On the contrary, patients with a positive isoproterenol-test showed no rise in plasma beta-endorphin levels (baseline 7.9+/-3.6 vs. syncope 7.4+/-2.7 pmol l(-1); P=ns). Patients with a passive negative tilt test (baseline 6.7+/-2.8 vs. end of test 7.0+/-3.3 pmol l(-1); P=ns) and negative isoproterenol tilt test (baseline 7.4+/-3.8 vs. end of test 8.1+/-3.4 pmol l(-1); P=ns) showed no changes in beta-endorphin concentrations. To further examine the efficacy of i.v. naloxone to prevent syncope, 10 patients were randomized to naloxone (0.02 mg/kg) or placebo. Second head-up tilt testing was negative in 1/5 patients with naloxone and in 2/5 patients with placebo. We conclude that, (1) endogenous opioids seem to be involved in vasovagal syncope induced by baseline head-up tilt test, (2) changes in plasma beta-endorphin concentrations show significant differences between patients who have isoproterenol-dependent and isoproterenol-independent syncope, this finding might occur in the setting of different pathophysiologic mechanisms, and (3) intravenous naloxone at a dose of 0.02 mg/kg was not superior to placebo in order to prevent positive responses to baseline tilt test.

[Long-term prognosis of patients with syncope of unknown origin in prolonged asystole induced by the head-up tilt test]

INTRODUCTION AND OBJECTIVES

Prognosis and therapeutic assessment of patients with syncope and prolonged asystole during head-up tilt test remain unclear. The aim of the present study was to analyze the clinical evolution of patients with syncope of unknown origin, no heart disease and severe cardioinhibitory response induced by head-up tilt.

METHODS

A prospective follow-up study was performed in 12 patients (6 male and 6 female, mean age 31 +/- 20 years) with recurrent syncope, no heart disease and affected by severe cardioinhibitory syncope induced by head-up tilt test. This was defined as syncope or near-syncope induced by baseline or isoproterenol tilt with asystole of > or = 3 seconds. All patients were re-tilted twice: with salt and fluid and with metoprolol (25 mg/b.i.d). According to the results of these tests, 5 patients were discharged with dietetic measures (salt & fluid) and 5 with metoprolol. In 2 patients who showed recurrent prolonged asystole a DDD pacemaker was implanted.

RESULTS

After follow-up of 34 +/- 20 months all patients ae alive. The number of recurrences was small (2 syncopes and 2 near-syncopes). No relationship was observed between the number of syncopal recurrences and the applied treatment.

CONCLUSIONS

We conclude that prolonged asystole induced by head-up tilt test does not confer an adverse prognosis in patients with syncope of unknown origin and no heart disease, thus, the clinical evolution of these patients is benign.

Cardiac pacing for vasovagal syncope: a reasonable therapeutic option?

A number of studies have evaluated the effect of cardiac pacing for prevention of tilt induced vasovagal syncope. The findings are relatively consistent. Pacing does not prevent the onset of vasovagal syncope. This is predictable since hypotension (vasodepressor effect) typically occurs prior to bradycardia. However, dual chamber may prolong the presyncopal period in patients with a prominent cardioinhibitory component. Further, the relation of laboratory observations to spontaneous events is uncertain. In the largest retrospective assessment of pacing efficacy, 89% of patients reported improved symptoms and 62% remained free of symptom recurrence over 50 months.

Head-up tilt test. A nonspecific method of evaluating patients with bifascicular block

BACKGROUND

Patients with bifascicular block have an increased risk of syncopal attacks, but the underlying mechanism often remains unclear despite an extensive diagnostic workup. The head-up tilt test has been established as an important diagnostic tool in the unmasking of vasovagal syncope in patients with unexplained syncope. Its role in the evaluation of patients with bifascicular block has not been studied.

METHODS AND RESULTS

A head-up tilt test, using a 60 degrees angle of tilt for 45 minutes without pharmacological provocation, was performed in 25 patients with bifascicular block and syncope that remained unexplained after an extensive invasive and noninvasive electrophysiological investigation. As a control group, 25 subjects with bifascicular block without syncope, matched for age, sex, left ventricular function, and underlying heart disease, were included. A positive head-up tilt test was found in 7 (28%) of the syncope patients and in 8 (32%) of the control subjects (P = NS). Six patients, of whom 3 had a positive tilt test, had recurrent syncopal attacks during 32 months of follow-up. None of the control subjects had syncope during follow-up.

CONCLUSIONS

This study gives rise to serious concern regarding the specificity of the head-up tilt test in patients with bifascicular block. A head-up tilt test should therefore be interpreted with caution, and its role as a diagnostic tool in this patient category remains to be established.

Cardiac pacing during neurocardiogenic (vasovagal) syncope

Head-up tilt testing is increasingly being used as a diagnostic modality in patients with unexplained syncope who are thought to have neurocardiogenic (vasovagal) mechanisms of syncope. Although large-scale placebo-controlled trials are still awaited, pharmacologic therapy is usually effective in preventing syncope or presyncope in this patient population. However, the role of permanent pacemaker therapy remains controversial. Because hypotension is usually associated with paradoxical bradycardia and occasionally asystole, it has been argued that permanent pacemaker therapy may be useful in preventing syncope and, thus, injury, in the so-called "malignant vasovagal cardioinhibitory response" in which the onset of syncope is thought to be abrupt. The onset of hypotension, however, usually precedes bradycardia during neurocardiogenic syncope, and pacing may thus not prevent syncope or presyncope in these patients. The role of cardiac pacing in patients with neurocardiogenic syncope is reviewed.

The clinical spectrum of neurocardiogenic syncope

Neurocardiogenic syncope is a collective term used to describe the clinical syndromes of syncope that result from inappropriate, and often excessive, autonomic reflex activity, and manifest as abnormalities in the control of vascular tone and heart rate. These include carotid sinus syndrome, vasovagal syncope, and the syndromes of cough, deglutition, and micturition syncope. Orthostatic hypotension, which, in contrast, results from a failure of autonomic reflexes, is not considered part of this family of closely related syndromes. This review will focus on vasovagal and carotid sinus syndromes.

Pathophysiological aspects of neurocardiogenic syncope: current concepts and new perspectives

Neurocardiogenic syncope is both a common and complex clinical disorder. Although recent research has clarified some of the pathophysiological mechanisms involved, much still remains either unknown or incompletely understood. Further investigation into this condition will not only enhance our knowledge of this and other related disorders, but will shed greater light on the influences of the brain and autonomic system on heart rate and blood pressure regulation and aid in our understanding of the complex interrelationships of neurocardiology.